[webkit-dev] Cross-platform fonts for Layout Tests

[Eric Seidel]

So are we saying it's impossible to have matching results across all
platforms if a test involves any text (in any font)?

I know it's certainly possible to have pixel-results for tests which
do not involve text match across all platforms (like SVG or images or
css styling, etc.)

Or is all this just theory?

-eric

On Mon, Jun 6, 2011 at 8:09 PM, Hao Zheng <zhenghao at chromium.org> wrote:
> Yes, actually in Skia, Chromium/Linux uses a noop gamma implementation
> in SkFontHost_gamma_none.cpp; however, if you use a substantial
> implementation in SkFontHost_gamma.cpp, there will be much image
> mismatch on Chromium/Linux for every font including Ahem. The slight
> differences are on font fringe.
> And I think if other WebKit is not using Skia at all, there will
> surely be even more differences.
>
> As the gamma implementation on Clank is desired, we should not fix
> this bug. Just file the bug to record this difference.
>
> On Fri, Jun 3, 2011 at 2:30 AM, Tony Chang <tony at chromium.org> wrote:
>> Perhaps, but in practice, it's not enough.  Here's an ahem pixel test that
>> is slightly different on Mac and Chromium Linux:
>> http://trac.webkit.org/browser/trunk/LayoutTests/platform/mac/fast/block/basic/010-expected.png
>> http://trac.webkit.org/browser/trunk/LayoutTests/platform/chromium-linux/fast/block/basic/010-expected.png
>>
>> Also, I think it would be hard to tell by examining the HTML if a test uses
>> another font.  For example, the line height of an empty block might depend
>> on the default font that isn't specified (does <pre></pre> render the same
>> height on all platforms?).
>> On Thu, Jun 2, 2011 at 10:44 AM, Adam Barth <abarth at webkit.org> wrote:
>>>
>>> I thought the whole point of Ahem was to avoid those problems.
>>>
>>> Adam
>>>
>>>
>>> On Thu, Jun 2, 2011 at 1:29 AM, Hao Zheng <zhenghao at chromium.org> wrote:
>>> > Actually, even the same Ahem font will be rendered differently on
>>> > different platform, depending on the font drawing library, the
>>> > anti-aliasing algorithm, subpixel, tiny float-point calculation diff
>>> > on different arch.
>>> >
>>> > On Thu, Jun 2, 2011 at 3:30 AM, Eric Seidel <eric at webkit.org> wrote:
>>> >> I know that Ahem is safe to use across multiple platforms (the font
>>> >> metrics
>>> >> will be the same).  Do we know if there are any other fonts for which
>>> >> this
>>> >> is true?
>>> >> I'd like to make the style-bot yell at people when they use pixel tests
>>> >> with
>>> >> non-safe fonts.  Right now that list would only include ahem.
>>> >> -eric
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>>> >>
>>> >>
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>>
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